Sources of contaminants and groundwater quality in the coastal part of a river delta

Assessment of possible sources that control the groundwater quality was carried out in the Cauvery deltaic region, India, since domestic and agricultural water requirements are largely met by groundwater abstraction. Major ion and bromide contents are high in groundwater in the coastal wells. Spatial and vertical distributions of ions reveal that the shallow wells and wells in coastal parts have high chloride, nitrate, ammonium and phosphate. Groundwater quality assessment was carried out using the prescribed limits of World Health Organization and Bureau of Indian Standards which indicates that 55 % of samples are not fit for drinking. Integrated suitability map for drinking was created based on the concept that if the water sample exceeds any one of the standards by World Health Organization or Bureau of Indian Standards, the well is not fit for drinking. Groundwater quality for agricultural activities was assessed using electrical conductivity, sodium adsorption ratio, residual sodium carbonate, United States salinity laboratory diagram and Food and Agricultural Organization methods. According to Food and Agricultural Organization, 84 % of samples are classified as low sodium water and are suitable for all crops and soils. It was found that the water quality in this area is affected by improper disposal of waste, sewage/drainage canals near the wells, irrigation return flow, application of agrochemicals and saline water intrusion in the coastal region. Further, integrated suitability map produced in this study will be useful for future groundwater development and planning in this area. The suitability map needs to be updated periodically for proper management plan to preserve the groundwater resource in this region